linux-kernel - Re: [PATCH v2] arm64: Kconfig.platforms: Enable GPIO_DAVINCI for ARCH

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Message-ID: <20190628203752.rdb6vvc42qd5ofgd@kahuna>
Date:   Fri, 28 Jun 2019 15:37:52 -0500
From:   Nishanth Menon <nm@...com>
To:     Keerthy <j-keerthy@...com>
CC:     <t-kristo@...com>, <will.deacon@....com>,
        <catalin.marinas@....com>, <shawnguo@...nel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <lokeshvutla@...com>
Subject: Re: [PATCH v2] arm64: Kconfig.platforms: Enable GPIO_DAVINCI for
 ARCH_K3

On 09:08-20190628, Keerthy wrote:
[..]
> > > +	select GPIO_SYSFS
> > > +	select GPIO_DAVINCI
> > 
> > 
> > Could you help explain the logic of doing this? commit message is
> > basically the diff in English. To me, this does NOT make sense.
> > 
> > I understand GPIO_DAVINCI is the driver compatible, but we cant do this for
> > every single SoC driver that is NOT absolutely mandatory for basic
> > functionality.
> 
> In case of ARM64 could you help me find the right place to enable
> such SoC specific configs?

Is'nt that what defconfig is supposed to be all about?

arch/arm64/configs/defconfig

> 
> > 
> > Also keep in mind the impact to arm64/configs/defconfig -> every single
> > SoC in the arm64 world will be now rebuild with GPIO_SYSFS.. why force
> > that?
> 
> This was the practice in arm32 soc specific configs like
> omap2plus_defconfig. GPIO_SYSFS was he only way to validate. Now i totally
> understand your concern about every single SoC rebuilding but now where do
> we need to enable the bare minimal GPIO_DAVINCI config?

Well, SYSFS, I cannot agree testing as the rationale in
Kconfig.platform. And, looking at [1], I see majority being mandatory
components for the SoC bootup. However, most of the "optional" drivers
go into arm64 as defconfig (preferably as a module?) and if you find a
rationale for recommending DEBUG_GPIO, you could propose that to the
community as well.

Now, Thinking about this, I'd even challenge the current list of configs as
being "select". I'd rather do an "imply"[2] - yes, you need this for the
default dtb to boot, however a carefully carved dtb could boot with
lesser driver set to get a smaller (and less functional) kernel.

> 
> v1 i received feedback from Tero to enable in Kconfig.platforms. Hence i
> shifted to this approach.

I noticed that you were posting a v2, for future reference, please use
diffstat section to point to lore/patchworks link to point at v1 (I
did notice you mentioned you had an update, thanks - link will help
catch up on older discussions). This helps a later revision reviewer
like me to get context.

Tero, would you be able to help with a better rationale as to where the
boundaries are to be in your mind, rather than risk every single
peripheral driver getting into ARCH_K3?

As of right now, I'd rather we do not explode the current list out of
bounds. NAK unless we can find a better rationale.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/Kconfig.platforms
[2] https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt

-- 
Regards,
Nishanth Menon